Si2401
12
Preliminary Rev. 0.9
Functional Description
The Si2401 is a complete modem chipset with
integrated direct access arrangement (DAA) that
provides a programmable line interface to meet global
telephone line requirements. Available in two 16-pin
small-outline packages, this solution includes a DSP
data pump, modem controller, codec, and DAA.
The modem accepts simple modem AT commands and
provides connect rates up to 2400 bps full-duplex over
the Public Switched Telephone Network (PSTN) with
V.42 hardware support through HDLC framing. To
minimize handshake times, the Si2401 can implement a
V.22-based fast connect. The modem also supports the
V.23 reversing protocol and standard alarm formats
including SIA.
This device is ideal for embedded modem applications
due to its small board space, low power consumption,
and global compliance. The Si2401 solution integrates a
silicon DAA using Silicon Laboratories’ proprietary third-
generation DAA technology. This highly-integrated DAA
can be programmed using the Si3010 to meet
worldwide PTT specifications for ac termination, dc
termination, ringer impedance, and ringer threshold.
The DAA can also monitor line status for parallel
handset detection and overcurrent conditions.
The Si2401 is designed for rapid assimilation into
existing modem applications. The device interfaces
directly through a UART to a microcontroller. The
Si2401URT-EVB evaluation board connects directly to a
standard RS-232 interface. This allows for evaluation of
the modem immediately upon powerup via
HyperTerminal or any standard terminal software.
The chipset can be fully programmed to meet
international telephone line interface requirements with
full compliance to FCC, TBR21, JATE, and other
country-specific PTT specifications. In addition, the
Si2401 has been designed to meet the most stringent
worldwide requirements for out-of-band energy, billing-
tone immunity, high voltage surges, and safety
requirements.
Table 7. Selectable Configurations
Configuration
Modulation
Carrier
Frequency (Hz)
Data Rate
(bps)
Standard
Compliance
V.21
FSK
1080/1750
300
Full
V.22
*
DPSK
1200/2400
1200
Full
V.22bis
*
QAM
1200/2400
2400
No retrain
V.23
FSK
1300/2100
1200/75
Full; plus reversing
(Europe)
V.23 1300/1700
600/75
Bell 103
FSK
1170/2125
300
Full
Bell 212A
DPSK
1200/2400
1200
Full
Security
DTMF
—
40
Full
SIA—Pulse
Pulse
—
Low
Full
SIA Format
FSK
1170/2125
300 half-duplex
300 bps only
*Note:
The Si2401 only adjusts its DCE rate from 2400 bps to 1200 bps if it is connecting to a V.22-only (1200 bps only)
modem. Because the V.22bis specification does not outline a fallback procedure, the host should implement a
fallback mechanism consisting of hanging up and connecting at a lower baud rate. Retraining to accommodate
changes in line conditions that occur during a call must be implemented by terminating the call and redialing.
